1. Field of the Invention
The present invention relates to chemical mechanical polishing (CMP). More particularly, the present invention relates to a pad conditioner of a semiconductor chemical mechanical polishing apparatus.
2. Description of the Related Art
In general, many layers such as semiconductor layers, insulation layers, and conductive layers must be formed on a semiconductor substrate to fabricate a semiconductor device. In addition, the surfaces of these layers must often be planarized on the semiconductor substrate. A chemical mechanical polishing (CMP) process is predominantly used in semiconductor device fabrication for planarizing such surfaces on a semiconductor substrate.
To perform the CMP process, a semiconductor substrate known as a wafer is transferred to a rotating polishing pad and an abrasive slurry is applied between the wafer and the polishing pad. The slurry causes a chemical reaction with the surface of the wafer. Also, the surface of the wafer is pressed against the rotating polishing pad, whereby the wafer is mechanically polished. As a result of these chemical and mechanical workings, the surface on the semiconductor substrate is planarized.
The polishing pad must have a uniform surface roughness to provide the desired polishing rate. Over time, however, the polishing process glazes the polishing pad and creates irregularities in the polishing pad. Accordingly, the polishing pad surface is typically conditioned by a pad conditioner to deglaze the surface of the polishing pad, whereby surface irregularities are removed and the slurry is capable of spreading uniformly across the polishing pad.
The pad conditioner typically consists of a conditioning head having a diamond disk with a roughened surface, a rotary actuating device for rotating the conditioning head, and a linear actuating device for driving the conditioning head up and down. First, the conditioning head is moved onto the polishing pad. And then the conditioning head is rotated against the polishing pad while being forced downwardly by the actuating devices, thereby conditioning the polishing pad.
In the conventional pad conditioner, the rotary actuating device includes a timing belt and a motor for driving the timing belt, and the linear actuating devices includes air supply tubing and a source of compressed air for forcing air through the tubing. However, over time, the timing belt becomes worn out or torn at a portion thereof with a pulley. When these problems occur, the rotational force can not be transferred to the conditioning head from the motor. Furthermore, the air supply tubing gradually degrades to the point where air begins to leak therefrom, especially at a joint of the tubing. In this case, sufficient air pressure can not be produced to move the conditioning head vertically.
In any case, pad conditioning can not be performed uniformly and normally when the timing belt or the air supply tubing is damaged. At the very least, damage to the timing belt or air supply tubing increases the time required for conditioning the polishing pad. Such damage also may produce particles that migrate onto the polishing pad, and thereby ultimately causing scratches on the semiconductor substrate surface.
Accordingly, the ability to test the timing belt and air supply tubing of the conditioning pad for signs of damage would be highly desirable.
Therefore, an object of the present invention is to provide a pad conditioner which is capable of monitoring itself for damage, whereby the conditioning rate and efficiency of the pad conditioner can be maintained.
According to one aspect of the present invention, a pad conditioner includes a housing, a conditioning head having a diamond disk for conditioning a polishing pad and mounted to the housing so as to be roatable and vertically movable relative to the housing, a transmission mechanism for transmitting a drive force from a motor to the conditioning head to rotate the conditioning head, an air supply system for supplying air pressure that moves the conditioning head vertically so that it can be forced against a polishing pad, and at leat one sensor for sensing the rotational speed of the conditioning head and/or the pressure of air being delivered to the conditioning head.
The transmission mechanism includes a first (drive) pulley which is rotated by a motor mounted to the housing, a second (driven) pulley connected to the conditioning head by a shaft, and a timing belt reeved around the first pulley and the second pulley. Preferably, the sensor is a rotation sensor installed near the second pulley and detecting the state of rotation of the conditioning head by sensing the rotational speed of the second pulley. The rotation sensor can be a flag sensor or an optical sensor.
The air supply system includes an air supply tube extending through said housing and through which air is supplied to the conditioning head. The sensor may thus be a pressure sensor installed on the air supply tube.
According to another aspect of the present invention, the operation of the polishing pad conditioner is monitored as follows. The conditioning head is first into contact with the polishing pad of a CMP apparatus. Then, the conditioning head is forced against the polishing pad with a certain pressure. While the conditioning head is forced against the polishing pad, the conditioning head is rotated by driving a transmission element coupled to the conditioning head.
Next, the pressure used to force the conditioning head against the polishing pad and/or the rate at which the transmission element is driven is/are sensed. The value of the sensed pressure and/or rate is/are compared to a corresponding value(s) representative of a normal operation of the polishing pad conditioner.